Investigation of initiation and early tissue formation in functionalized scaffold for vavular tissue regeneration

Description

In situ tissue engineering (TE) using a biodegradable synthetic scaffold that recruits endogenous cells from the bloodstream is emerging as a promising technology to create living heart valves inside the human body having the potential to last a life-time. In situ TE is heavily reliable on the wound healing response. The biomaterial intensifies the inflammatory response by inducing a foreign body response, propagated by infiltrating immune cells. However inflammation is not merely a detrimental response to the implanted scaffolds. Rather, it can be considered as a natural agent of tissue remodeling, orchestrated by various cell types and potent signaling molecules. By unraveling the inflammatory response towards the foreign biomaterial and the triggers for pathological outcome, targets may be identified to control the inflammatory response through modifications of the biomaterial.

The inflammatory process starts with the rapid infiltration of the scaffold by monocytes. Monocytes differentiate into macrophages, which in turn attract progenitor cells that differentiate into tissue-producing cells. Macrophages act as primary mediator cells throughout the healing cascade by transiently stimulating inflammation, repair and resolution. Macrophages are highly plastic cells that can attain various reversible polarization states depending on local biochemical environment. During the first stages of the inflammatory process, macrophages activated are typically of the M1 phenotype. Their activation is stimulated by pro-inflammatory cytokines, e.g. IFN-γ and TNF-α. M1 macrophages are crucial in intracellular pathogens killing, matrix destruction and tissue reorganization. Contrariwise alternatively activated macrophages, i.e. M2a and M2b, are involved in wound healing and regulatory process. M2a and M2b are stimulated by the release of anti-inflammatory cytokines as IL-4, IL-10, TGF-β and IL-13 (Fig.1). By promoting the M2 phenotype, either via specific recruitment or local polarization, the inflammatory process may instantly be directed towards healing instead of inflammation.

The goal of the project is to quantitatively understand the role of one of the key regulatory cytokines, i.e. IL-4, in order to predict the outcome of the inflammatory process and to control the delicate balance between fibrotic or functional regenerated ECM production. The effect of the IL-4 boosted natural human host response on early tissue formation will be investigated in vitro. Data will be used to allow the development of an IL-4 loaded synthetic scaffold that selectively activates the wound healing M2 phenotype.

Temporal macrophages phenotypic features and tissue formation over time will be assessed with a mesofluidic setup mimicking the hemodynamic conditions of the natural host response to the implanted scaffold. Moreover, the scaffold will be exposed to mechanical forces to further investigate previous results showing a strain-dependent modulation of macrophages polarization.